Various types of operating circuits are known to operate and start fluorescent lamps. One type of circuit uses an inductance and a serially connected blocking capacitor, both connected in the current supply circuit of the lamp and, in the starting circuit, a starting capacitor to the lamp, that is, connected serially with the heating electrodes of the lamp. It has also been proposed--see the referenced U.S. Pat. No. 2,231,999--to provide a temperature-dependent resistor serially connected to the starting capacitor in the starting circuit.
Various starting circuits for low-pressure discharge lamps utilize a glow-type starter to preheat the lamp electrodes. The glow-type starter is connected in the ignition or starting circuit. It has been found that, upon first connecting the lamp, a glow discharge or flash occurs until the starter circuit operates and preheating begins. This glow discharge may be perceived in form of flicker, which is annoying and undesirable.
Compact fluorescent lamps, and fluorescent lamps in general of low power, may have starter and ballast circuitry integrated in the base of the lamp, or the socket therefor. The lamp is desirably operated at a frequency high with respect to power line frequency. High-frequency operation is suitable. High-frequency operation eliminates undesirable flicker and light variation of the lamp, particularly during ingition or starting. This flicker is effectively avoided by including a resonant circuit in the starting circuitry--see the referenced literature "Elektronikschaltungen" ("Electronic Circuitry") by Walter Hirschmann, Berlin/Munich, SIEMENS Aktiengesellschaft, 1982, p. 148.
By suitable selection of the capacitor in the resonance circuitry, it is possible to adjust the idle voltage of the lamp for desirable and optimum conditions, within certain limits. In compact fluorescent lamps, it is desirable to maintain the voltage on the resonant capacitor, and therefore on the lamp electrodes, at a level which is so low that, upon first connecting the lamp, the otherwise occurring glow discharge will not occur. On the other hand, however, the voltage, after sufficient preheating, should be so high that the lamp will reliably fire or ignite, even if ambient temperatures are low, and below usual "room temperature".
U.S. Pat No. 2,231,999, Gustin et al., describes a circuit arrangement for the ignition circuit of a fluorescent lamp utilizing a series circuit of a resonance capacitor and a temperature-dependent resistor. The temperature-dependent resistor is of the negative temperature coefficient type, that is, upon first connecting the resistor to electrical power, its resistance is high. As current flows through the resistor, and the resistor becomes hot, the resistance of the resistor decreases. In dependence on the characteristics of the NTC resistor, the lamp will, eventually, ignite or fire.
In the operation of this curcuit, initially, a small preheating current will flow. The preheating time of the lamp, thus, is long. At low ambient temperatures, the voltage across the lamp may not be sufficient to cause ignition reliably. After ignition, a relatively high current will flow through the ingnition circuit. This reduces the overall efficiency of the system, since continuous heating of the electrodes results only in wasting of power. Additionally, the electrodes may overheat, which leads to increased consumption of emission material customarily placed on the electrodes, which reduces the lifetime of the lamp and further decreases light output thereof due to blackening of the glass walls.